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R. T. Zavala

Publications and source records attributed to R. T. Zavala.

38 records · Page 3Linked to original sources
arXiv2001

Time Variable Faraday Rotation Measures of 3C-273 and 3C-279

Multifrequency polarimetry with the VLBA confirms the previously reported time-varying Faraday rotation measure (RM) in the quasar 3C-279. Variability in the RM and electric vector position angle (EVPA) of the jet component (C4) is seen making it an unreliable absolute EVPA calibrator. 3C-273 is also shown to vary its RM structure on 1.5 year time-scales. Variation in the RM properties of quasars may result from a Faraday screen which changes on time-scales of a few years, or from the motion of jet components which sample spatial variations in the screen. A new component emerging from the core of 3C-279 appears to be starting to sample such a spatial variation. Future monitoring of this component and its RM properties is suggested as a diagnostic of the narrow line region in 3C-279. We also present a new method of EVPA calibration using the VLA Monitoring Program.

astro-ph↗
arXiv2001

Discovery of Radio Emission from the Brown Dwarf LP944-20

Brown dwarfs are classified as objects which are not massive enough to sustain nuclear fusion of hydrogen, and are distinguished from planets by their ability to burn deuterium. Old (>10 Myr) brown dwarfs are expected to possess short-lived magnetic fields and, since they no longer generate energy from collapse and accretion, weak radio and X-ray emitting coronae. Several efforts have been undertaken in the past to detect chromospheric activity from the brown dwarf LP944-20 at X-ray and optical wavelengths, but only recently an X-ray flare from this object was detected. Here we report on the discovery of quiescent and flaring radio emission from this source, which represents the first detection of persistent radio emission from a brown dwarf, with luminosities that are several orders of magnitude larger than predicted from an empirical relation between the X-ray and radio luminosities of many stellar types. We show in the context of synchrotron emission, that LP944-20 possesses an unusually weak magnetic field in comparison to active dwarf M stars, which might explain the null results from previous optical and X-ray observations of this source, and the deviation from the empirical relations.

astro-ph↗